Hydraulic draft tube



Mall, 1929. L, Q Y 1,113,775

HYDRAULIC DRAFT TUBE Filed Nov. 2a. 1922 5 Sheets-Sheet 1 May 21, 1929.L, MOODY 1,713,775

HYDRAULIC DRAFT TUBE Filed Nov. 28, 1922 5 Sheets-Sheet 2 May 21, 1%29.1 MOODY 1,713,775

HYDRAULIC DRAFT TUBE Filed Nov. 28 1922 5 Sheets-Sheet s oawtoz May 21,1929 F, MOQDY 1,713,775

HYDRAULIC DRAFT TUBE Filed Nov. 28, 1922 5 Sheets-Sheet 5 INVENTOR 7Zvm%/ Patented May 21, 1929.

UNITED STATES LEWIS FERRY MOODY, 0F PHILADELPHIA, PENNSYLVANIA.

. HYDRAULIC DRAFT TUBE.

Application filed November 28, 1922. Serial No. 608,769.

This invention relates to hydraulic turbines and in particular to animproved means for receiving water from the turbine runner anddelivering it to the tail race. More particularly my invention relatesto means of this character wherein the water is turned or spread outfrom a direction along the axis of the runner into diverging radialdirections and is subsequently turned into a single radial-direction fordischarge into the tail race.

In many modern hydraulic power plants the turbines are placed in a rowwith vertical shafts, the water entering the turbines on one side of therow from the penstocks or forebay and discharging at the other side intothe tail race. The water leaves the runners in a downward direction athigh velocity and some means should be provided which will reduce thisvelocity so as to correspondingly reduce the back pressure on theturbine runners and which will likewise turn the flow into a horizontaldown stream direction. This means should be constructed so as to performthese functions without appreciable losses of energy and should itselfoccupy a minimum space. The last condition is particularly desirable inorder that the turbines themselves may be closely spaced and the powerhouse dimensions made as small as possible.

For the purpose of reducing the velocity, draft tubes have been usedwhich direct the flow from the runner radially outward on spreadinglines and discharge it horizontally in every direction. The flow maythen be received by a collector which turns it into a common down-streamdirection. Certain portions of the flow must be turned throughsubstantially 180 while other portions, which leave the tube in adirection more nearly approaching the down-stream do not have to beturned through so great an angle.

If an unlimited space were available the initial. velocity with whichthe water enters the draft tube could be reduced and its kinetic energyturned into effective head for the turbine by the use of the spreadingaction alone, that is, the water could be discharged outwardly in alldirections at such a low velocity that but little kinetic energy wouldremain in it. The problem of collecting the flow and discharging itdown-stream would be solved by the use of any suitable collector whichwould not cause an appreciable loss of head.

With the available space limited, however, it is desirable to provide adraft tube of such dimensions that the water discharged into thecollector will retain a portion of its kinetic energy and that thecollector be so designed as to reduce further the velocity of the waterand to regain this energy. The water leaving the draft tube in anLip-stream direction may be conveniently collected from the tube by oneor more spiral passages extending circumferentially around thecylindrical outlet of the tube and discharging tangentially down streamtoward the tail race.

These spiral passages should be enlarged at a rate greater than isnecessary to accommod-ate the cumulative flow so that the velocity ofthe flow therethrough will be gradually reduced.

One of the objects of the present invention is to provide an improvedcollector of this character which is designed to receive a flow ofconsiderable velocity from the draft tube and is adapted gradually anduniformly to reduce the velocity of this flow and so regain its kineticenergy. 7

Another object of my invention is to provide in addition to the spiralcollector passages above described an effective means for deceleratingthat portion of the flow which does not enter the spiral passages.

Numerous other objects and advantages will appear from the followingdescription taken in connection with the accompanying drawings whichillustrate certain of the preferred embodiments of my invention andwherein Fig. 1 is a view showing vertical sections of a draft tube andcollector taken on the line 11 of Fig. 2 looking in the direction of thearrows.

Fig. 2 is a view. showing a horizontalsection on the line 22 of Fig.1.

Fig. 3 is a View similar to Fig. 1 but showing a slightly modifiedconstruction.

Fig. 4 is a view showing a vertical section, on the line 4-4 of Fig. 5,of a still further modified form of my invention.

Fig. 5 shows a horizontal section taken on line 5--5 of Fig. 4.

Fig. 6 a vertical section on the line 6-6 of Fig. 5.

Fig. 7 which is a sectional View on line 7-7 ofFig. 8 shows a stillfurther modification.

Fig. 8 is a horizontal sectional view on the line 8-8 of Fig. 7.

Fig. 9 shows avertical sectional" view on thelin'e' 9-9 of Fig. 8;

Fig. 10 shows a vertical section taken on the line 101O of Fig.3 lookingin thedirec-,

tion of the arrows;

Fig. 11 shows in vertical section on the line 12-12 of Fig. 11.

Fig. 13 a vertical section the line'.13"13 of Fig. 12.

Fig. '14 a vertical section on the line l l la 01' Fig. 12 taken in thedirection of the arrows. Fig. 15 represents a vertical section on line15-15 of Fig. 16 and shows a modification in the form and'arrangement ofthe collector passage and- J V Fig; 16 'showsa section on line 1616otFig.15.

Referring to Figs. 1 and 2 reference character 20 indicates generallytheprimary draft tubeand 21 the collector. The primary draft tube asshownistormed of an outer wall 22 havingja slightly tapered or conical upperportion 23 and gradually curved outward to a"horizontaldirection at itslower end. Projecting upwardly from the floor 25 of the collectorpassage into the flaring end of the wall 22 and concentric'therewith isa cone 26 whose concave surface is formed in relation to the outline ofthe flared end of the wall 22. The outer wall and cone'i lti' togetherform the primary draft tube which serves to direct the flow downwardfrom the turbine run-- ner and outwardly into a horizontal plane. Thecross sectional areaof this tubeas shown increases gradually so as togive a gradual decelerationto the meridian components of thefiow, and attheysame time the tube is adapted-to handle ei'i'ic-iently flowcontaining whirling;components about the turbine axis.

The outer wall or the tube is cut away to form the collector passage 21,the material around the outer wall of the tube'thus forminga projection28, depending intothe collector chamber. The general contour of thebottom otthis projection is shown in Fig. 2 by the'line 29. Thisprojection joins the side wall 30 or" the collector passage at a point31 farthest removed from the tail water and is formed with a verticalside wall joining its bottom with the upper wall 33 of the'collectorchamberat a point 32 nearest the tail water. Between these twodiametrically opposite points the side wall of the projection 28'slopesinwardly a horizontal distance represented hy'the distancebetween thelines 29 and 35 in Fig. 2, thus forming a channel 36 which lies above oroverhangs the flared portion of the draft tube. The outer side wall30 ofthe collector chamber recedes from the "projection 28st) as to provide apassage of constant- 1y increasing area which will take care of the Itwill be noted that the water flowing out otthe draft tube in the generaldown-stream direction does not pass upward into the overhangingchannel36 but flows for a certain distance betwen two flatsurfacesformed by the fioor 25 and the bottom of theprojection 28. In so flowingit difiuses and isspread laterally in a general direction indicated bylines 10? and er of Fi 2. Water flowing laterally and water which flowsin. anupstream direction from the draft tube will turn upwardly to tillthe passage 36. The lateral and upstream flows merge within passage 36and flow in a downstream direction therein. The new in the passage 36when reaching the downstream edge of member 28 (see Fig. 2) merges withthe downstream flow disposed between the bottom and the opposed surfaceof projection 28. There is thus provided, in effect, a separate passagefor the water leaving the draft tube in the down-stream direction andone which permits the flow to increase in area and consequently'todecrease in velocity. r

l t the rapidly moving water which is bein dischar item the draft tubein a downstream tlllebblOll which I will term the direct flow werepermittedto discharge directly into tail water or other wide open space,that-is, a space which does not provide for its gradual dillusion, thekinetic energy of the flow-would be lost. Furthermore it the direct flowwere permitted to mix with the slower moving water from the otherportions of the draft tube eddies andcros s-currents would be createdwhich would cause 7 a further loss of energy.

1n the form shown in Figs. 1 and 2 the upper. and lower surfaces betweenwhich the direct flow proceeds are parallel, while in Fig.3 lhaveinclinedthe upper surface 43 upwardly toward'tailwater by a small angle0: so as to give a greater reduction in velocity. The angle between theupper and lower surfaces should not exceed approximately 15 or inextreme cases 20, if an etlicient velocity conversion is to be secured.

1n the form of my invention shown in Figs. 4 to 6' Ihave maintained theouter wall of the projection 28- vertical or substantially vertical andso there is no overhanging channel 36 as shown in the prior figures. The1 upper wall of the collector chamber is curved upwardly as is indicatedat 1 1 in Fig. 6 to provide thenecessary increase in area. The lower endof the projection 28 in thesefigures has a different contour from thatshown in Fig. 2 as may be readily seen. In Fig. 5 the projection extendsmuch further down-stream and is joined at its extended end to the floorof the discharge passage by means of a'pier or partition 45. Thispartition is of such a form and is located at such a distance from thedischarge end of the tube as not to interfere with the direct flowtoward the tail water.

The structure shownin Figs. 4t to 6 is less expensive to build than thatshown in the previous figures and may be employed when somewhat morespace is available.

The curved collector passages shown in Figs. 1 to 6 are of the doublespiral type and are intended to be employed where the water isdischarged from the draft tube with only small degrees of whirl, thatis, such a structure is intended to be used with turbines of moderate orlow specific speeds. In the form of my invention shown in the remainingfigures I have provided for the collection of a whirling discharge.

In the form shown in Figs. 7 to 10 I provide a single curved collectorchannel which starts at a point 40 at the mouth of the draft tube, iscurved. around the axis of the tube through an angle of approximately180 and terminates in a straight passage 47 having a directiondownstream and substantially tangential to the draft tube. The inner andouter walls of this passage are vertical and its upper and lower wallshorizontal except that the upper wall of the outer passage is inclinedupward at an angle preferably not to exceed about 15.

The passage 4-9 for discharging the direct flow is substantiallyrectangular in. cross seetion and is formed by the floor 25, top wall 50which is inclined upwardly at an angle not to exceed about 20, side wall51 and wall 52, the last being formed by a partition 53 which separatesthe passage for the direct flow from the end of the curved passage.

It will be noted that the draft tubes as shown in Figs. 7 and 9 are muchshorter than those shown in the previous figures and do not havetheintermediate straight conical portion between the runner and thebeginning of the spreading portion.

The form of my invention shown in Figs. 11 to 14 is similar to thatshown in Figs. 7 to 10 except in the former the curved collector passagedoes not terminate in a straight section but continues to curve so thatthe total curve exceeds 180 and also continues to flare horizontallythrough its entire course. This passage is quite narrow but considerablyhigher than those shown in previous figures.

The partition of Figs. 7 and 8 is omitted, there being merely a strut 56between the upwardly extending top wall of the passage for the directflow and the floor 25. The cone shown in this form of my inventionextends upwardly through the entire draft tube to the runner and therunner shown is of the propeller type. If desired the form shown inthese figures may have the over-hanging passage collector shown in Fig.1.

In Figs. 15 and 16 I have shown a modified construction and arrangementof collector for use where lateral space is limited. The collectorpassage here shown surrounds the outlet of the draft tube and extendsdownwardly therefrom and under the cone 60. The form of the inner wallof. the expanding collector passage beneath the cone is indicated by theline 61 beginning at the point 62 where this wall joins the outer wall63and ending at 64 at the outlet While I have shown a primary draft tubewhich is constructed to progressively increase in area in certain casesit may be. necessary to employ one whose principal function is to turnthe water outwardly in all directions without being able to produce anysubstantial decrease in velocity. 'With theuse of such tubes it would benecessary to employ a collector which will reduce the velocity of theflow from an amount which is only slightly less than its velocity at therunner.

Moreover even with these turbines wherein the discharge velocity fromthe spreading conduit is suiiiciently small to be sothrown away when theturbine is operating at its normal capacity, it must be considered thatunder the usual conditions turbines are frequently called upon tooperate at capacities considerably above normal and when so operatingthe discharge velocity from the spreading conduit rapidly increases andmay represent a very material amount of velocity head in comparison withthe available head on the plant. A failure to provide for efficientdeceleration of this yelocity of discharge from the spreading or primarydraft tube may therefore materially restrict the full-load *apacity ofthe turbine even in cases where the primary or spreading conduit issutlicient in itself to take care of the ordinary and normal loadconditions with high eificiency. The proper formation of the collectorpassages therefore may have a vital effect upon the full power capacityof the turbine.

It should also be considered that by providing efficient collectorpassages the size of the primary portion of the draft tube may be cutdown without serious loss of draft tube efficiency, but with a materialreduction in the over-all dimensions of the entire draft tube, andconsequently of the power-house and substructure.

lVhile I have shown my invention as applied to turbines having verticalaxes it is obvious that with slight modification of structure myinvention is likewise applicable to turbines having horizontal shafts. Ihave also shown a draft tube and collector which receive water in anaxial direction and dis charge it in a radial or tangential direction,that is. along a plane at substantially right angles to the axis of thedraft tube. It is of course apparent that the angle between the axis andthe discharge direction need not be- ;present invention as set forth Iedclaims-t 7 5 exactly a right angle'as conditions of practice might makeit desirableLto increase or decrease thisangle somewhat. U Z V WVh1le inthe foregoing ClBSOIIPt ZLOIL I have distinguished between theprimarydraft tube and the. collector, 1t willberecognized that in otherforms of my invention the primary draft tub'eand collector functionmaybeso merged-that no one portion of the struc ure may be termed aprimary draft tube and the remainder a collector. Such casesmaynevertheless fall clearly within the scope of the in theappe'ncb inginto said horizontal passage and said wall havlng a port on elongated ina downstream direction to form a roof extension inthe horizontalpassage, whereby said horizontal. passagecomprisesa relatively deep sidepassage and a relatively shallow passage, the

body portion of saiddown stream portion bcing so shaped asto ;lieentirelyinside of'a straight horizontal ;lineicontacting with any pointof aside surface of saidbody portion.

2; A draft tube for hydraulic turbines, comprising vertical andhorizontal passages, said vertical passage having a wall projecting'intosaidhorizontal passage and said wall having a portionelongated in a downstream direction to form a roof extension in the horizontalpassage,-whereby sa d horizontal passage comprises a relatively deepside passage and a, relatively shallow passage, the body portion of saiddown stream portion being so shaped'as to lie entirely inside of astraight horizontal line contactingwithany point of a sidesurface of.said body portion, the upstreamwall of said horizontal passagebeingsubstantially tangent to one point of theontletiof said verticalpassage. I

3, A draft tube for. hydraulic turbines, comprising substantiallyvertical and horizontal passages, said vertical pass geihaving a wallprojecting into said horizontal,pas

sageand said wall having a portion cion-' gatedin a down streamdirection toform a froof extension in the horizontal passage 7 wherebythere are formed relatively deep side "passages and .a'trelativelyshallow central passage, the body portion of said down stream extensionbemg so shaped as to he entirely inside of a straight horizontal line'contact- 7 ing with any point of the sidesurfaces of said body portion.7 I

A draft tube for hydraulic-turbines,

shaped,

' at. A draft tube for hydraulic turbines,

comprising substantially vertical and hor1- zontal passages, saidvertical-passage having a wall projecting into said horizontalpassage toprovide an outlet for the vertical passage, said projecting wall beingelongated in a down stream directionto form an offset e roof, wherebysaid horizontalqpassage includes passages having upper surfaces (118*posed at different elevations, the body portion of saidprojected'walland its elongated portion being so shaped, as to heentirely 1nside of a'aight horizontal line contacting vwith any point of a side surface ofsaid body portion. p Y.

5. A draft tube for hydraulic turbines, comprising substantiallyvertically and horizontally extending walls forming substantiallyvertical. and horizontal passages, said verti cal wall projectingintosaid horizontal-pas. sage and extending up and down-stream, the

- n of said projection down-stream being reater than that Lip-stream,and th ebody r portion of said projecting Wall and itsdown streamproje'ction'being so shaped asto lie entirely inside of a straighthorizontal line contactin with any point of the side surfaces ofsaidbody portions j. l

i 6. A draft tube for hydraulic turbines, comprising substantiallyvertically and horizontally extendin g Walls forming substantially,vertical and horizontal passages, said vertical wall projecting intosaid horizontal passageand extending up and down-stream, the dnnension.of said pro ection down-stream being greaterthan that up-stream and thebody portion of said projecting wall and its downstream projectionsbeing so shaped as to lie entirely inside of a straight horizontal linecontacting with any pointof the side surfacesof said body portion, andthe floor of said horizontal passage. and the under surface of saiddownstream extension being relatively diverged. l a r a a 7. A drafttube 'for hydraulic turbines comprising a horizontal passageprovidedwith a roof' and floors, and a vertical passage projecting into saidhorizontal passage and having a flared end the forward part of which iscontinued forwardly to form a longitudinal roof extension disposedatalower elevation than that of said'other roof, and said floor and roofextension being relatively diverged and thebody portioniof saidprojecting wall and its downstream projection being so shaped as to lieentirely inside of a straight horizontal line contacting with any pointof the side surfaces of said body portion. is v 8.7 A draft tube for -,ahydraulic turbine, comprising a horizontal passage and a verticalpassage having a wall projecting into said horizontal passage, therip-stream side of said well being. of generally elliptical formationwhile its down-stream side-iris 'wedge 9. A draft tube for a hydraulicturbine, comprising a horizontal passage and a vertical passage having awall projecting into said' wall being of generally elliptical formationwhile its down-stream side is wedge shaped, and means forming aprojection extending laterally from said wall.

11. In a turbine, a draft tube having a radially spreading verticalpassage provided with an outlet, and a collector passage having a spiralside wall beginning adjacent the outlet of said vertical passage andhaving a portion occupying space lying nearer to the axis of saidvertical passage than the outlet thereof, a direct discharge portionforming a downstream continuation of the vertical passage outlet andadapted to decelerate the flow between upper and lower surfaces, and alateral projection extending substantially the length of said directdischarge portion.

12. In a turbine, a draft tube having a radially spreading verticalpassage provided with an. outlet and a collector having a spiral sidewall beginning adjacent the outlet of said vertical passage and having aportion occupying space above the outlet of vertical passage tube andnearer to the axis thereof than said outlet is, a direct dischargeportion forming a down-stream continuation of the vertical passageoutlet and adapted to de celerate the flow between upper and lowersurfaces, and a lateral projection extending the full length of saiddischarge portion.

13. In a turbine, a draft tube having a radially spreading verticalpassage provided with an outlet and a collector adapted to receive waterfrom said vertical passage at a considerable velocity and to cause saidwater to be continuously decelerated, said collector occupying spaceabove and within the radial limits of the outlet of said verticalpassage, and having a spiral side wall beginning adjacent the out-let ofsaid vertical passage, a direct discharge portion forming a downstreamcontinuation of the vertical passage outlet adapted to decelerate theflow between upper and lower surfaces.

14. In a turbine, a draft tube having a radially spreading verticalpassage provided with an outlet and a collector adapted to receive waterfrom said vertical passage at a considerable velocity and to cause saidwater to be continuously decelerated, said col lector occupying spaceabove and within the radial limits of the outlet-of said draft tubevertical passage, and having a' spiral side wall beginning adjacent theoutlet of said vertical passage, a direct discharge portion forming adown-stream continuation of the vertical passage outlet and adapted todecelcrate the flow between upper and lower surfaces, and a lateralprojection extending the full length of said discharge portion.

15. A draft tube having means for discharging water radially insubstantially all directions, means for conducting the water dischargedin one direction between fiow surfaces which diverge by an angle notexceed ing 20, and means for collecting the water discharged in otherdirections and conducting it through a channel of increasing areawhereby it is turned into the said one direction and its velocitydiminished.

16. The combination in a draft tube comprising a radially spreadingvertical passage provided with an outlet and a collector formed of twospiral. passages which are arranged to receive water discharged fromsaid vertical passage in substantially all directions except a generaldown-stream direction, said vertical passage having a wall projectinginto said collector to form the outlet of said vertical passage, andsaid wall,

having a continuation in a down stream direction to form a roof of apassage to receive and conduct, toward the tail race, water dischargedin a downstream direction from said vertical passage, said continuationhaving a port-ion extended radially with respect to the main bodyportion thereof and the outer edge of one portion having a curvaturedifferent from that of the outer surface of the other portion, and allof said passages gradually increasing inarea at such rates that thevelocity head of the flow entering said passage is efficiently convertedinto pressure head.

17. A draft tube for hydraulic turbines, comprising walls formingsubstantially vertical and horizontal passages, the wall of saidvertical passage projecting into said horizontal passage and beingturned so as to extend up and downstream, the dimension of saiddownstream project-ion being greater than that upstream and the bodyportion of said projecting wall and its downstream projection being soshaped as to lie entirely inside of a straight horizontal linecontacting with any point of the side surfaces of said body portion,while the side surfaces of said downstream projection have verticalportions of material depth.

18. A draft tube for hydraulic turbines, comprising walls formingsubstantially vertical and horizontal passages, the, wall of saidvertical passage projecting into said horizontal passage and beingturned so as to extend up and downstream, the dimension of saiddownstream projection being greater than that upstream and the bodyportion of: said projecting Wall and its downstream pro-' jection beingso shaped as to lie'entirely in-' side of a straight horizontal linecontacting With any point of the side surfaces of said body portion,whereby said horizontal passage has twolateralpassages which are dis--posed entirely above the ffloor of said horizontal passage. .7 q

19. A draft tube for hydraulic turbines,

comprising Walls forming substantially vertical and horizontal passages,the Wall of said vertical passage projecting into said horizontalpassageand being turned so-as to extend up and downstream thedimension of saiddownstream projection being greater than that upstream and thebodyportion of said projecting all and its downstream pro:

jectionbei'ng so shaped as tolie entirely inside of a straighthorizontal line contacting with any point of the side surfaces of said.

body portion, whereby said-horizontal passage has two lateral passagesof greater depth than the passage beneath the said. downstreamprojection and said lateral passages being disposed substantiallyentirely above the flow of said passage beneath the downstream proection.

LEWIS FEa YMeon CERTIFICATE OF CORRECTION.

Patent No. 1,713, 775. Granted May 21, 1929, to

LEWIS FERRY MOODY.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 6,line 27, claim 19, for the word "flow" read "floor"; and that the saidLetters Patent should be read with this correction therein that the samemay conform to the record of the case in the Patent Office.

Signed and sealed this 30th day of July, A. D. 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents.

